1. Technical Field of the Invention
The present invention relates to a photo interrupter including a light emitting portion and a light receiving portion for detecting the presence or absence of an object therebetween. Of such photo interrupters, the present invention particularly relates to a photo interrupter of the kind which can be surface-mounted on a printed circuit board, for example. The invention further relates to a method for manufacturing such a photo interrupter.
2. Description of the Related Art
Photo interrupters utilizing a metal lead frame are conventionally known, and recently surface-mounting types, which can be fixed to a printed circuit board by soldering, has been developed.
As disclosed in JP-A-11-274550 for example, such a surface mount type photo interrupter includes an insulating substrate, and a light emitting element and a light receiving element mounted on the upper surface of an insulating substrate and hermetically sealed by respective transparent sealing members. On the lower surface of the insulating substrate, a pair of terminal electrodes for the light emitting element and a pair of terminal electrodes for the light receiving element are formed, which are utilized for surface-mounting the photo interrupter on a printed circuit board. The photo interrupter further includes a cap bonded to the upper surface of the insulating substrate. The cap includes two hollow portions respectively accommodating the light emitting element and the light receiving element sealed by the transparent sealing members, and a groove formed between the two hollow portions for receiving an object to be detected. The light emitted from the light emitting element passes across the groove of the cap to reach the light receiving element.
In this kind of photo interrupter, the light emitting element and the light receiving element of are sealed by transparent sealing members mainly for the purpose of enhancing the durability.
However, in the above-described prior-art surface mount type photo interrupter, to seal the light emitting element and the light receiving element on the insulating substrate individually by respective transparent sealing members, a transparent resin layer of a thickness capable of covering the light emitting element and the light receiving element is first formed on the entire upper surface of the insulating substrate. The transparent resin layer is then divided into a sealing member for the light emitting element and that for the light receiving element by dicing in the vertical direction and the horizontal direction.
Therefore, the sealing of the light emitting element and the light receiving element by respective sealing members requires a large number of process steps, which leads to an increase in the manufacturing cost. Further, there is a large possibility that a conductor pattern formed on the insulating substrate is damaged in the dicing in two directions, which results in a defective product.
Moreover, as noted above, in the prior-art surface mount photo interrupter, the light emitting layer and the light receiving layer are mounted on an insulating substrate and sealed by sealing members, and a cap is bonded to the insulating substrate. Since the insulating substrate has a single layer structure and hence has a relatively low rigidity, the insulating substrate may be warped or deformed due to an external force or due to the difference in thermal expansion between the sealing transparent resin and the cap.
When the insulating substrate is warped or deformed, and hence, a gap is formed between the upper surface of the insulating substrate and the cap bonded thereto, part of the light emitted from the light emitting element may leak through the gap to directly reach the light receiving element without passing across the groove in which an object to be detected is placed. In such a case, the presence or absence of the object cannot be detected precisely.